NBC’S LOOSE RATINGS GRIP: NBC has won the ratings race in the 18-49 demographic the last two seasons. So why does its reign feel tenuous? Perhaps because NBC hasn’t had a breakout hit in a few years and relies on “The Voice” and “Sunday Night Football” to prop up its numbers, as The Wall Street Journal reports. Sports rights aren’t cheap and reality shows don’t last forever, so every network needs new hits to compete with each other and streaming services. NBC could really use a show like the intriguing “Blindspot” to pop among viewers. Really, so could any of the big broadcast networks, which is why they are promoting...